Novel cyanine dyes for the sensitization of organic photoconductors



United States Patent Ofice 3,542,548 Patented Nov. 24, 1970 US. Cl.96--1.6 33 Claims ABSTRACT OF THE DISCLOSURE Organic photoconductors arespectrally sensitized with a cyanine dye having apyrrolo[2,3-b]quinoxaline nucleus or a pyrrolo[2,3-b]pyrazine nucleus,joined at the 3-carbon atom thereof, to the methine linkage of thecyanine dye.

This invention relates to electrophotography, and more particularly tomaterials and elements useful in the electrophotographic process.

Elements useful in the electrophotographic process commonly comprise anelectrically conductive support bearing a stratum including aphotoconductive insulating layer which has a resistivity substantiallygreater in the dark than in light actinic thereto. Such elements can beused in electrophotographic processes, for example, by first adaptingthe element in the dark to obtain a uniformly high resistivity in thephotoconductive insulating layer, and electrostatically charging theelement in the dark to obtain a relatively high potential which may beeither negative or positive in polarity. The element can then be exposedto a light pattern which lowers the resistivity and thereby the chargedensity of the illuminated areas imagewise in proportion to theintensity of illumination incident upon each point of the illuminatedareas. A latent electrostatic image is obtained. Visible images can beformed from the latent electrostatic image in any convenient manner,such as by dusting with a finely divided, fusible pigment the particlesof which bear an electrostatic charge opposite that remaining on thesurface of the photoconductive insulating layer. Thereafter, the pigmentparticles can be fused to the surface to provide a permanent image.

Various photoconductive substances have been employed in photographicelements and processes of the type described above. Typical inorganicphotoconductive materials include selenium and zinc oxide. Suchinorganic photoconductive materials have irfiierent disadvantages, suchas an inability to be readily adapted totreflex copying systems, or toproduce images on transparent supports except by indirect means. Organicphotoconductors avoid such disadvantages, but generally have relativelypoor sensitivity to visible radiation. It has been proposed to increasethe spectral sensitivity of organic photoconductors with certain cyanineor merocyanine dyes, for example, such as those listed in Table Dhereinafter. The spectral sensitivity imparted by such dyes is weak. It,therefore appears highly desirable to provide effective spectralsensitizers for organic photoconductors.

One object of this invention is to provide novel sensi tized organicphotoconductors.

Another object of this invention is to provide novel spectrallysensitized organic photoconductor materials.

Still another object of this invention is to provide novel compositionsof matter comprising organic photoconductors and certain spectralsensitizers.

A further object of this invention is to provide novel compositions ofmatter comprising organic photoconductor, binder and certain spectralsensitizers for the organic photoconductor.

Still another object of this invention is to provide a novelelectrophotographic material including a conductive support havingcoated thereon an insulating layer containing spectrally sensitizedorganic photoconductor.

A further object of this invention is to provide methods for spectrallysensitizing organic photoconductors.

Still other objects of this invention will be apparent from thefollowing disclosure and the appended claims.

In accordance with one embodiment of this invention, novel compositonsof matter are provided comprising organic photoconductors spectrallysensitized with the dyes defined more fully below. These compositionscan be incorporated in a suitable binder and coated on a conductivesupport for use in electrophotography.

In another embodiment of this invention, compositions of matter areprovided comprising organic photoconductors spectrally sensitized withthe dyes described below, dispersed in an insulating binder. Thesecompositions of matter can be coated on a conductive support and used inelectrophotographic processes.

In still another embodiment of this invention, electrophotographicmaterials are provided comprising a conductive support having coatedthereon a layer comprising an insulating binder, an organicphotoconductor and a spectral sensitizing quantity of a dye defined morefully below.

In another embodiment of this invention, a method is provided forspectrally sensitizing organic photoconductors which comprises mixing adye of the type described below with an organic photoconductor, in aconcentration sufiicient to effectively spectrally sensitize the organicphotoconductor. Preferably, the dye and organic photoconductor are mixedin a suitable solvent.

The spectral sensitizing dyes which are employed in this invention arecertain cyanine dyes containing certain pyrazole nuclei which, whenincorporated in a test negative gelatin silver bromoiodide emulsionconsisting of 99.35 mole percent bromide and .65 mole percent iodide, ata concentration of 0.2 millimole of dye per mole of silver halide,desensitize the emulsion more than 0.4 log B when the test emulsion iscoated on a support, exposed through a step wedge in a sensitometer (toobtain D to light having a wavelength of 3165 mm., processed for threeminutes at 20 C. in Kodak Developer D-19, and is fixed, washed anddried. As used herein and in the appended claims, the test negativesilver bromoiodide emulsions are prepared as follows:

In a container with temperature control is put a solution with thefollowing composition:

G. Potassium bromide Potassium iodide 5 Gelatin 65 Water, 1700 cc.

And in another container is put a filtered solution consisting of:

G. Silver nitrate 200 Water, 2000 cc.

3 stirrer. The precipitation is conducted over a period of minutes.

The developer employed in the test referred to above is Kodak DeveloperD-l9 which has the following composition:

G. N-methyl-p-arninophenol sulfate 2.0 Sodium sulfite, desiccated 90.0Hydroquinone 8.0 Sodium carbonate, monohydrated 52.5 Potassium bromide5.0

Water to make 1.0 liter As indicated above, the cyanine dyes employed inthis invention desensitize conventional negative silver halideemulsions. Such emulsions are inherently sensitive to blue radiation.The present dyes reduce that sensitivity. In addition, these dyes failto provide practical spectral sensitization for such emulsions.Therefore, it was quite unexpected to find that they spectrallysensitized organic photoconductors.

Another characteristic of the cyanine dyes of this invention is thatthey are substantially non-photoconductive. The term substantiallynon-photoconductive as used herein means that no image is formed when asolution of 0.002 g. of the dye and 0.5 g. of polyester binder(described in Examples 1 to 2 below) are dissolved in 5.0 ml. ofmethylene chloride, and is coated and tested (in the absence of anyphotoconductor) as described in Examples 1 to 2 below.

The cyanine dyes of this invention increase the speed of organicphotoconductors by extending or increasing the response of thephotoconductor to visible radiation (i.e., radiation in the range ofabout 400 nm. to 2700 nm.) In the concentrations used, the dyes hereinappear to function as spectral sensitizers when employed with efiicientorganic photoconductors. When the organic photoconductor used is poor orinefficient, the dyes seem to function as speed increasing compounds aswell as spectral sensitizers.

The cyanine dyes that are useful in practicing the invention includethose comprising first and second 5- to 6-membered nitrogen containingheterocyclic nuclei joined together by a methine linkage containing from2 to 3 carbon atoms in the methine chain (including those link- 4 ageswherein a methine group is substituted by alkyl, aryl or heterocyclicsubstituents); the first of said nuclei being selected from apyrrolo[2,3-b]quinoxaline nucleus or a pyrrolo[2,3-b1pyrazine nucleusjoined in each case at the 3-carbon atom thereof to said linkage; and,said second nucleus being selected from (a) a heterocyclic nitrogencontaining nucleus of the type used in the production of cyanine dyes,when said linkage is a dimethine linkage, and (b) when said linkage is atrimethine linkage, said second nucleus is selected from the groupconsisting of a Z-arylindole nucleus, a pyrrolo[2,3-b]quinoxalinenucleus and a pyrrolo[2,3-b1pyrazine nucleus, each of said nuclei beingjoined at the 3-carbon atom thereof to said trimethine linkage, tocomplete said cyanine dye. Preferably, the second nucleus is anelectron-accepting nucleus.

The preferred cyanine dyes that are useful herein include thoserepresented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L represents amethine linkage, e.g., --Cl-I=, -C (CH -C(C H -C(3indolyl)=;C(2-pyridyl)=;

4 'C(2-thienyl)=; etc.; R represents an alkyl group, includingsubstituted alkyl, (preferably a lower alkyl containing from 1 to 4carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl,cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups,(preferably a substituted lower alkyl containing from 1 to 4 carbonatoms), such as a hydroxyalkyl group, e.g., fl-hydroxyethyl,w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., p-methoxyethyl,w-butoxybutyl, etc., a carboxyalkyl group e.g., fi-carboxyethyl,w-carboxybutyl, etc., a sulfoalkyl group, e.g., [3- sulfoethyl,w-sulfobutyl, etc., a sulfatoalkyl group, e.g., B- sulfatoethyl,w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., fl-acetoxyethyl,'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group,e.g., ,B-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or anaralkyl group, e.g., benzyl, phenethyl, etc.; an alkenyl group, e.g.,allyl, l-prophenyl, Z-butenyl, etc.; or, an aryl group, e.g., phenyl,tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc. R represents an alkylgroup, e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl,etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, etc.; R and Reach represents a hydrogen atom, an alkyl group (preferably a loweralkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl,isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an arylgroup e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl,methoxyphenyl etc.; and, R and R taken together with the two fusednuclei to which they are attached, can represent the non-metallic atomsnecessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R representsa hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl,chlorophenyl, nitrophenyl, methoxyphenyl, etc.; X represents an acidanion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate,perchlorate, ptoluenesulfonate, methyl sulfate, ethyl sulfate, etc.; andZ represents the non-metallic atoms necessary to complete, aheterocyclic nucleus of the type used in cyanine dyes, and preferably anelectron-accepting nucleus, containing from 5 to 6 atoms in theheterocyclic ring, which nucleus may contain a second hetero atom suchas oxygen, sulfur, selenium or nitrogen, such as the following nuclei: athiazole nucleus, e.g., thiazole, 4-methylthiazole, 4- phenylthiazole,S-methylthiazole, 5-phenylthiazole, 4,5-dimethylthiazole,4,5-diphenylthiazole, 4-(2-thienyl)thiazole, benzothiazole,4-chlorobenzothiazole, 4- or S-nitrobenzothiazole,5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole,4-methylbenzothiazole, 5- methylbenzothiazole, 6-methylbenzothiazole,6-nitrobenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole,S-chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole, 4-rnethoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole,5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole,S-ethoxybenzothiazole, tetrahydrobenzothiazole,5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole,S-hydroxybenzothiazole, 6- hydroxybenzothiazole, naphtho[2,1-d]thiazole,naphtho [1,2-d]thiazole, naphtho[2,3-d]thiazole,S-methoxynaphtho[2,3-d]thiazole, 5-ethoxynaphtho[l,2-d]thiazole, 8-methoxynaphtho [2,1-d]thiazole, 7-methoxynaphtho [2, ldJthiazole,4'-methoxythianaphtheno-7,6'4,5-thiazole, nitro group substitutednaphthothiazoles, etc.; an oxazole nucleus, e.g., 4-methyloxazole,4-nitro-oxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole,4-ethyloxazole, 4,5-dimethoxazole, S-phenyloxazole, benzoxazole,S-chlorobenzoxazole, S-methylbenoxazole, 5-phenylbenzoxazole, 5- or6-nitrobenzoxazo1e, 5-chloro-6-nitrobenz oxazole, 6-methylbenzoxazole,5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole,S-ethoxybenzoxazole, 5 -chlorobenzoxazole, 6-methoxybenzoxazole,S-hydroxybenzoazole, 6-hydroxybenzoxazole, naphth [2,1-d]oxazole,naphth[1,2-d]oxazole, nitro substituted naphthoxazoles, etc.; aselenazole nucleus, e.g., 4-methylselenazole, 4-nitroselenazole,4-phenylselenazole, benzo selenazole, S-chlorobenzoselenazole,S-methoxybenzoselenazole, S-hydroxybenzoselenazole, 5- or6-nitrobenzoselenazole, 5-chloro-6-nitrobenzoselenazole,tetrahydrobenzoselenazole, naphtho[2,1-d]selenazole, naphtho[1,2-d]selenazole, nitro substituted naphthoselenazoles, etc.; a thiazolinenucleus, e.g., thiazoline, 4-methylthiazoline, 4- nitrothiazoline, etc.;a pyridine nucleus, e.g., 2-pyridine, S-methyl-Z-pyridine, 4-pyridine,3-methyl-4-pyridine, nitro group substituted pyridines, etc.; aquinoline nucleus, e.g., 2-quinoline, 3-methyl-2-quinoline,5-ethyl-2-quinoline, 6- chloro 2 quinoline, 6 nitro 2 quinoline, 8chloro- 2 quinoline, 6 methoxy 2 quinoline, 8 ethoxy- 2 quinoline, 8hydroxy 2 quinoline, 4 quinoline, 6- methoxy-4-quinoline,6-nitro-4-quinoline, 7-methyl-4- quinoline, 8-chloro-4-quinoline,l-isoquinoline, 6-nitro-1- isoquinoline, 3,4-dihydro-l-isoquinoline,3-isoquinoline, etc., a 3,3-dialkylindolenine nucleus, preferably havinga nitro or cyano substituent, e.g., 3,3-dimethyl-5 or 6-nitroindolenine,3,3-dimethyl-5- or 6-cyanoindolenine, etc., and, an imidazole nucleuse.g., imidazole, l-alkylimidazole, lalkyl-4-phenylimidazole, l-alkyl4,5-dimethylimidazole, benzimidazole, l-alkylbenzimidazole,1-aryl-5,6-dichlorobenzimidazole, l-alkyl-lH-naphthimidazole, 1-aryl-3H-naphth[1,2-d]imidazole, 1 alkyl S-methoxy-lH-naphth- [1,2 d]imidazole oran imidazo[4,5 b]quinoxaline nucleus, e.g.,1,3-dialkylimidazo[4,5-b]quinoxaline such as 1,3 diethylimidazo [4,5-b]quinoxaline, 6 chloro 1,3-diethylimidazo[4,5-b] quinoxaline, etc.,1,3-dialkenylirnidazo [4,5-b1quinoxaliue such as 1,3-diallylimidazo[4,5-b]quinoxaline, 6 chloro-1,3 diallylimidazo[4,5-b]quinoxaline, etc.,1,3-diarylimidazo[4,5-b]quinoxaline such as 1,3-diphenylimidazo [4,5 -b]quinoxaline, 6-ch1orol ,S-diphenylimidazo[4,5-b]quinoxaline etc.; a1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g.,1,3,3-trimethyl-3H-pyrrolo [2,3 -b] pyridine, 1,3 ,3-triethyl-3H-pyrrolo [2,3 -b] pyridine, etc.; a thiazole[4,5-b1quinoline nucleus; and the like. Nuclei wherein Z in aboveFormula I represents an imidazo[4,5-b]quinoxaline nucleus, a1,3,3-trialkyl-3H pyrrolo[2,3-b]pyridine nucleus, a thiazolo[4,5-b]quinoline nucleus, a nitro substituted thiazole, oxazole,selenazole, thiazoline, pyridine, quinoline, 1,3,3-trialkylindolenine,or imidazole nucleus are electron-accepting nuclei. Dyes such as definedabove containing such nuclei are the preferred spectral sensitizing dyesfor photoconductor compositions and elements of this invention.

As used herein and in the appended claims, electron accepting nucleusrefers to those nuclei which, when converted to a symmetricalcarbocyanine dye and added to a gelatin silver chlorobromide emulsioncontaining 40 mole percent chloride and 60 mole percent bromide, at aconcentration of from 0.01 to 0.2 grams dye per mole of silver, cause byelectron trapping at least about an 80 percent loss in the blue speed ofthe emulsion when sensitometrically exposed and developed three minutesin Kodak developer D-19 at 20 C., the composition of which is givenabove. Preferably, the electron-accepting nuclei are those which, whenconverted to a symmetrical carbocyanine dye and tested as just describedabove, essentially completely desensitize the test emulsion to blueradiation. Substantially complete desensitization as used herein,results in at least at 90 percent, and preferably a 95 percent loss ofspeed to blue radiation.

Another highly useful class of cyanine dyes that function as spectralsensitizers in this invention include those represented by the followinggeneral formula:

wherein R R R R R and X are as previously defined, R represents an alkylgroup (preferably a lower alkyl containing from 1 to 4 carbon atoms),e.g., methyl,

ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl etc.,or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl,nitrophenyl, methoxyphenyl, etc., or a heterocyclic radical containingfrom 5 to 6 atoms in the heterocyclic ring and having a hetero nitrogen,oxygen or sulfur atom, preferably a heterocyclic radical selected frompyridyl (e.g., 2-, 3- or 4-pyridyl), 3-indolyl, of 2-thienyl; Rrepresents a hydrogen atom or an aryl group, e.g., phenyl, tolyl,naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; and Drepersents the non-metallic atoms necessary to complete a 2-arylindolenucleus (e.g., a 1-a1kyl (or aryl)-2-phenylindole, a l-alkyl (or aryl)-5nitro-Z-phenylindole, etc.) a pyrrolo[2,3-b]quinoxaline nucleus (e.g.,1-butyl-7-chloropyrrolo[2,3-b]quinoxaline,1-methyl2-p-tolylpyrrolo[2,3-b1quinoxaline, etc.) or apyrrolo[2,3b]pyrazine nucleus (e.g., 1-methylpyrrolo[2, 3-b]pyrazine,etc.).

The cyanine dyes defined by Formula I above are conveniently prepared,for example, by heating a mixture of wherein R R R and R are aspreviously defined, in approximately equimolar proportions, in a solventmedium such as acetic anhydride. The crude dyes are separated from thereaction mixtures and purified by one or more recrystallizations fromappropriate solvents such as methanol alone or acidified with an acidsuch as p-toluenesulfonic acid, perchloric acid, etc.

The intermediates defined by Formul IV above may be prepared by means ofthe Vilsmeier reaction. For example by reacting (1) a compound of theformula:

or a compound of the formula:

wherein R R R R and X are as previously defined, with (2) a complex ofphosphoryl chloride, phosgene, oxalyl chloride, etc., and dimethylformamide, in excess dimethylformamide as solvent, in approximateproportions of 1 mole of (1) to 3 or more moles of (2). The reactionmixtures are cooled, diluted with an ice-water mixture, and then madealkaline by addition of aqueous allgali metal hydroxide solution such asaqueous sodium hydroxide. The product is then separated by conventionalmethods, for example, by extraction of the mixture with awater-insoluble solvent such as chloroform, the residue being purified,if desired, by one or more re- '7 crystallizations from appropriatesolvents such as dimethyl formamide.

The cyanine dyes defined for Formula II above are conveniently prepared,for example, by heating a mixture of (l) a compound of Formula IV aboveand (2) a compound of the formula:

(VII) wherein D, R R and R are as previously defined, in approximatelyequimolar proportions, in a solvent medium such as acetic anhydridescontaining a strong mineral acid such as perchloric acid. After coolingand diluting with ether, the solid which separates is recrystallized.

Further details for the preparation of the dyes herein can be had byreference to our copending application Ser. No. 705,595, filed Feb. 15,1968, wherein such dyes and their preparations are described.

Included among the dyes defined above are the following typical dyecompounds. The method for preparing Dye No. I is included in Table Abelow to illustrate, in general, how the dyes herein are prepared.

pyrrolo[2,3 b]quinoxalinoearboeyanine bromide.

(VIII). 1-buty1-7-ehloro-1,3-trimethyl5-nitroindo-3-pyrrolo[2,3-b]quinoxalinocarboeyanine bromide.

(IX) 3-ethyl-1-methyl-6 -nitro-2-p-tolyl-3-pyrr0l0-[2,3 b]-quinoxalinothiacarbocyanine p-toluenesuli'onate.

(X) 1,3-diallyl-1-methyl-Zp-tolylimidaz0[4,5 b]quin0xalino-3-pyrrolo[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate.

(XI) 6-ehloro-1-methyl-1,3-di henyl-2-p-tolylimidazo-[4,5-b]

quinoxalino-3-pyrrolo 2,3-b]quinoxalino-earbocyanninep-toluenesulfonate.

(XII) 1,1,3,3-tetramethyl-5-nitro-2-p-t0lylindo-3-pyrr0l0[2,3b]-

quinox alinocarbocyanine p-toluenesulfonate.

(XIII)- 1,1',3,3-tetramethyl-2-p-tolylpyrrolo[2,3-b] pyrido-3-pyrrolo2,3-b1quinoxacarbocyannine perchlorate.

(XIV) 1,1-dimethyl-2,8-diphenyl-W-ptolyl-Zt-indolo 3-pyrrolo[2,3-b]quinoxaliuoearbocyanine perchlorate.

Dye N0.

mide. (XXVIII)S-ethyl-l,1-dimethyl-5,6-diphenyl-3-pyrrol0[2,3-b]pyrazino-3'-pyrrolo[2,dbl-quinoxalinocarbocyanine bromide. (XXIX)Zethyl-I,1-dimethyl-S-(Z-naphthyl)-3,3-pyrrolo[2,3-b]

pyrazinoearbocyanine bromide.

Compound 1 l-ethyl 3 forlnylpyrrolo[2,3-b1quinoxaline (0.56 g., 1 mol.)and 3-ethy1'2-methy1-6-nitrobenz0thiazolium p-toluenesulfonate (0.99 g.,1 mol.) in acetic anhydride (10 ml.) are heated at reflux for 1 minute.The cooled solution is slowly diluted with excess ether and the solidwhich is precipitated is collected and washed with ether. After onerecrystallization from methanol, the yield of purified dye is 0.77 g.(51%), M.P. 2Sl282 C., dec.

Dyes such as illustrated above can be used alone, or a combination ofone or more of the above described dyes can be used to impart thedesired spectral sensitivity. All of them are spectral sensitizers fororganic photoconductors. Suitable organic photoconductors which areeffectively spectrally sensitized by such dyes include both monomericand polymeric organic photoconductors. The invention is particularlyuseful in increasing the speed of organic photoconductors which aresubstantially insensitive, or which have low sensitivity (e.g., a speedless than but generally less than 10 when treated as described inExamples 1 to 6 below) to radiation in 400 to 700 nm.

An especially useful class of organic photoconductors is referred toherein as organic amine photoconductors. Such organic photoconductorshave as a common structural feature at least one amino group. Usefulorganic photoconductors which can be spectrally sensitized in accordancewith this invention include, therefore, arylamine compounds comprising(1) diarylamines such as diphenylamine, dinaphthylamine,N,N'-diphenylbenzidine, N-phenyl-l-naphthylamine;N-phenyl-Z-naphthylamine; N,N-diphenyl-pphenylenediamine; 2-carboxy 5chloro-4'-methoxydiphenylamine; p-anilinophenol;N,N'-di-2-naphthylp-phenylene diamine; 4,4 benzylidenebis(N,N-diethylm-toluidine), those described in Fox U.S. Pat. No.3,240,- 597 issued Mar 15, 1966, and the like, and (2) triarylaminesincluding (a) non-polymeric triarylamines, such as triphenylamine,N,N,N,N'-tetraphenyl rn phenylenediamine; 4-acetyltriphenylamine,4-hexanoyltriphenylamine; 4 lauroyltriphenylamine;4-hexyltriphenylamine, 4 dodecyltriphenylamine, 4,4bis(diphenylamino)-benzil, 4,

4'-bis(diphenylamino)-benzophenone, and the like, and (b) polymerictriarylamines such as poly[N,4- (N,N',N' triphenylbenzidine)];polyadipyltriphenylamine, polysebacyltriphenylamine;polydecamethylenetriphenylamine; poly N (4-vinylphenyl)-diphenylamine,poly N (vinylphenyl)-u,a'-dinaphthylamine and the like. Other usefulamine-type photoconductors are disclosed in U.S. Pat. No. 3,180,730,issued Apr. 27, 1965.

Other very useful photoconductive substances capable of being spectrallysensitized in accordance with this in vention are disclosed in Fox U.S.Pat. No. 3,265,496, is-

sued Aug. 9, 1966, and include those represented by the followinggeneral formula:

wherein A represents a mononuclear or polynuclear divalent aromaticradical, either fused or linear (e.g., phenylene, naphthylene,biphenylene, binaphthylene, etc.), or a substituted divalent aromaticradical of these types wherein said substituent can comprise a membersuch as an acyl group having from 1 to about 6 carbon atoms (e.g.,acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxygroup having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy,propoxy, pentoxy, etc.), or a nitro group; A represents a mononuclear orpolynuclear monovalent aromatic radical, either fused or linear (e.g.,phenyl, naphthyl, biphenyl, etc.); or a substituted monovalent aromaticradical wherein said substituent can comprise a member, such as an acylgroup having from 1 to about 6 carbon atoms (e.g., acetyl, pro pionyl,butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms(e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from1 to about 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or anitro group; Q can represent a hydrogen atom, a halogen atom or anaromatic amino group, such as A'NH-; b represents an integer from 1 toabout 12, and G represents a hydrogen atom, a mononuclear or polynucleararomatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituentcomprises an alkyl group, an alkoxy group, an acyl group, or a nitrogroup, or a poly(4-vinylphenyl) group which is bonded to the nitrogenatom by a carbon atom of the phenyl group. Certain nitrogen heterocycliccompounds are also useful photoconductors in the invention such as, forexample, 1,3,5-triphenyl-2-pyrazo1ine, 2,3, 1,5- tetraphenylpyrrole,etc.

Polyarylalkane photoconductors are particularly useful in producing thepresent invention. Such photoconductors are described in US. Pat. No.3,274,000; French Pat. No. 1,383,461 and in a copending application ofSeus et al., Ser. No. 624,233, Photoconductive Elements ContainingOrganic Photoconductors filed Mar. 20, 1967. These photoconductorsinclude lcucobases of diaryl or triaryl methane dye salts,1,1,l-triarylalkanes wherein the alkane moiety has at least two carbonatoms and tetraarylmethanes, there being substituted an amine group onat least one of the aryl groups attached to the alkane and methanemoieties of the latter two classes of photoconductors which arenon-leuco base materials.

Preferred polyaryl alkane photoconductors can be represented by theformula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, analkyl group, or an aryl group, at least one of D, E and G containing anamino substituent. The aryl groups attached to the central carbon atomare preferably phenyl groups, although naphthyl groups can also be used.The aryl groups can contain substituents such as alkyl and alkoxy,typically having 1 to 8 carbon atoms, hydroxy, halogen etc. in theortho, meta or para positions, ortho-substituted phenyl being preferred.The aryl groups can also be joined together or cyclized to form afluorene moiety, for example. The amino substituent can be representedby the formula wherein each R can be an alkyl group typically having 1to 8 carbon atoms, a hydrogen atom, an aryl group, or together thenecessary atoms to form a heterocyclic amino group typically having 5 to6 atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At leastone of D, E and G is preferably p-dialkylaminophenyl group. When I is analkyl group, such an alkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylallkane photoconductors include thecompounds listed below:

.. 4,4-bis(dimethylamino)-1,1,1-triphenylethanc.

(14) 1-(4-N,N-dimethylaminophenyl)-1,l-diphenylethane. (15)4-dimethylaminotetraphenylmethane. (13)4-diethylaminotetraphenyhnethane.

As described herein a wide variety of photoconductor compounds can bespectrally sensitized with the dyes referred to above. Some organicphotoconductors will, of course, be preferred to others; but in generaluseful results may be obtained from substantially all of the presentlyknown organic photoconductors.

The following Table C comprises a partial listing of US. patentsdescribing such organic photoconductors and compositions which can beused in place of those more particularly described herein.

TABLE 0 Patent Inventor Issued Numbers Noe et a1 Feb. 25, 1964 3,122,435 Sus et a1. Mar. 31, 1964 3,127, 266 Schlesinger Apr. 21, 1964 3,130,046 Cassiers Apr. 28, 1964 3, 131,060 Schlesinger June 30, 1964 3, 139,338 Do. June 30, 1964 3, 139, 339 Cassiers July 14, 1964 3, 140, 946Davis et a1 3, 141, 770 Ghys 3,148,982 Oassiers. 3, 155, 503 Do3,158,475 Tomanek. 3, 161, 505 Schlesinger 3, 163, 530 Do 3, 163,531 Do.3, 163, 532 Hoegl. 3, 169, 060 Stumpf 3,174, 854 Kluplel et al Apr. 27,1965.. 3, 180, 729 Do Apr. 27, 1965 3, 180, 730 Neugebauer- June 15,1965. 3, 189, 447 0 Sept. 14, 1965 3, 206, 306 July 21, 1964 3, 141, 770June 5, 1962 3, 037, 861 June 26,1962 3,041,165 Schlesinger 3, 066, 023he 3, 072, 476 Klupfel et al 3, 047, 095 Neugebauer at a 3, 112, 197Cassiers et al 3, 113, 022 Schlesinger 3, 114, 633 Kosche et a 3, 265,497 3, 274, 000

The quantity of the above-described dye required to spectrally sensitizean organic photoconductor varies with the results desired, theparticular dye used, and the particular organic photoconductor used.Best results are obtained with about .01 to parts by weight dye andabout 1 to 75 parts by Weight of the organic photoconductor based on thephotoconductive composition. Binder can be employed in suchcompositions, when desired, at preferred ranges of 25 to 99 parts byWeight. In addition, the composition can contain other sensitizers,either spectral sensitizers or speed increasing compounds, or both.

As used herein and in the appended claims, the terms insulating andelectrically conductive have reference to materials the surfaceresistivities of which are greater than 10 ohms per square unit (e.g.,per square foot) and less than 10 ohms per square unit (e.g., per squarefoot) respectively.

Coating thicknesses of the photoconductive compositions of the inventionon a support can vary widely. As a general guide, a dry coating in therange from about 1 to 200 microns is useful for the invention. Thepreferred range of dry coating thickness is in the range from about 3 to50 microns.

To produce a reproduction of an image utilizing the electrophotographicelements of our invention, the photoconductive layer is preferably darkadapted, and then is charged either negatively or positively by meansof, for example, a corona discharge device maintained at a potential offrom 60007000 volts. The charged element is then exposed to lightthrough a master, or by reflex in contact with a master, to obtain anelectrostatic image corresponding to the master. This invisible imagemay then be rendered visible by being developed by contact with adeveloper including a carrier and toner. The carrier can be, forexample, small glass or plastic balls, or iron powder. The toner can be,for example, a pigmented thermoplastic resin having a grain size of fromabout 1100,u which may be fused to render the image permanent.Alternatively, the developer may contain a pigment or pigmented resinsuspended in an insulating liquid which optionally may contain a resinin solution. If the polarity of the charge on the toner particles isopposite to that of the electrostatic latent image on thephotoconductive element, a reproduction corresponding to the original isobtained. If, however, the polarity of the toner charge is the same asthat of the electrostatic latent image, a reversal or negative of theoriginal is obtained.

Although the development techniques described hereinabove produce avisible image directly on the electrophotographic element, it is alsopossible to transfer either the electrostatic latent image, or thedeveloped image to a second support which may then be processed toobtain the final print. All of these development techniques are wellknown in the art and have been described in a number of U.S. and foreignpatents.

The following examples are included for a further understanding of theinvention.

EXAMPLES 1-2 These examples show the great increase in speed of organicphotoconductors when the dyes employed in this invention are addedthereto. This increase in speed is due to the spectral sensitivityimparted to the photoconductor by the dyes described herein. Theexamples also show that the maximum sensitivity peaks (Abs. max) occurin most cases at radiations in the region of the spectrum from about 480to 510 nm. A number of the dyes also impart more than one maximumsensitivity peak as illustrated by Example 1 in Table 1 hereinafter.

A series of solutions are prepared consisting of 5.0 ml. methylenechloride (solvent); 0.15 g. 4,4 bis(diethylamino)2,2-dimethyltriphenylmethane (organic photoconductor); 0.50 g. polyestercomposed of terephthalic acid and a glycol mixture comprising a 9:1weight ratio of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane and ethyleneglycol (binder) and 0.0065 g. of the spectral sensitizing dye indicatedby identifying number from above Table A. Each solution is coated on analuminum surface maintained at 25 C., and dried. All operations arecarried out in a darkened room. A sample of each coating is uniformlycharged by means of a corona to a potential of about 600 volts andexposed through a transparent member bearing a pattern of varyingoptical density to a 3000 K. tungsten source. The resultantelectrostatic image pattern is then rendered visible by cascading adeveloper composition comprising finely divided, colored, thermoplastic,electrostatically responsive toner particles carried on glass beads overthe surface of the element. The image is then-developed by deposition ofthe toner in an imagewise manner on the element. (Other developmenttechniques such as those described in U.S. 2,786,- 439; 2,786,440;2,786,441; 2,811,465; 2,874,063; 2,984,- 163; 3,040,704; 3,117,884; Re.25,779; 2,297,691; 2,551,- 582; and in RCA Review, vol. 15 (1954) pp.469-484, can be used with similar results.) An image is formed on eachsample, as indicated in Table I. Another sample of each coating istested to determine its electrical speed and maximum sensitivity peak.This is accomplished by giving each element a positive or negativecharge (as indicated in Table I) with a corona source until the surfacepotential, as measured by an electrometer probe, reaches 600 volts. Itis then exposed to light from a 3000 K. tungsten source of 20-footcandles at the exposure surface. The exposure is made through a steppeddensity gray scale. The exposure causes reduction of the surfacepotential of the element under each step of the gray scale from itsinitial potential, V0, to some lower potential, V, whose exact valuedepends on the actual amount of exposure in metercandle-seconds receivedby the area. The results of these measurements are plotted on a graph ofsurface potential V vs. log exposure for each step. The actual speed ofeach element is expressed in terms of the reciprocal of the exposurerequired to reduce the surface potential by volts. Hence, the speedsgiven in Table I are the numerical expression of 10 divided by theexposure in metercandle-seconds required to reduce the 600 volts chargedsurface potential by 100 volts. The results are shown in Table I below.

Referring to the above Table I, it Will be seen that the control examplecontaining the same photoconductor but no dye shows speeds of only 8 and7 for the positively and negatively charged surfaces, respectively,whereas, the corresponding values for those of the invention representedby Examples 1 to 2, are clearly of a diiferent order of magnitude. Forexample, the speed shown by Example 2 (Dye No. (II)) is 310 and 460 forthe positively and negatively charged surfaces, respectively, withmaximum sensitivity peak at 510 nm., thus indicating a speed increaseover that of the control by a factor of about 38 for the positivelycharged and about 65 for the negatively charged. Also of greatsignificance is the extension of the absolute sensitivity to the regionof 500 nm. In the case of Example 1 (Dye No. (1)) the improvement inspeed is also impressive in comparison with that of the control byfactors of about 25 and 28 for the positively charged and negativelycharged surfaces, respectively. Similar results are obtained when Dye(I) or Dye (II) is replaced with any one of Dyes ('III) through (XX), orany dye in the list following Table A.

Similar results to those shown in above Table I are obtained, when, forexample, the organic photoconductor 4,4bis(diethylamino)-2,2'-dimethyltriphenylmethane is replaced with 0.15 g.of triphenylamine (using the p toluenesulfonate salt of each dye), or1,3,5-triphenyl-2- pyrazoline, or 2,3,4,5-tetraphenylpyrrole, or4,4'-bis-diethylaminobenzophenone or when other dyes of the inventionembraced by Formula I above are used. These results show that the dyesof this invention effectively spectrally sensitize a wide variety oforganic photoconductors. The dyes of this invention are not inthemselves photoconductive. Also, it should be noted that the abovementioned photoconductors when used alone have very low photoconductivespeed to visible light. However, as shown by the tests, the combinationof the dyes of the invention with the photoconductors of the inventionprovide compositions and elements of outstanding speed and excellentquality of image.

This invention is highly unexpected because dyes previously suggestedfor spectral sensitizers impart weak spectral sensitization to organicphotoconductors. Typical dyes proposed by the prior art as spectralsensitizers, which produce weak spectral sensitization in these systems,are shown in Table D below.

TABLE D Dye identification: Name A) Pinacyanol.

(B) Kryptocyanine.

(C) Anhydro-3-ethyl-9 methyl-3'-(3- sulfobutyl thiacarbocyaninehydroxide.

(D) .3,3'-diethyl-9-methy1thiacarbocyanine bromide.

(E) 3-carboxymethyl-5-[(3-methyl-2- thiazolidinylidene)-1-methylethylidene]rhodanine.

(F) Anhydro-S,5'-dichloro-3,9 diethyl- 3'-( 3-sulfobutylthiacarbocyanine hydroxide.

(G) 1-ethy1-3-methylthia-2'-cyanine chloride.

(H) l,1-diethyl-2,2'-cyanine chloride.

In contrast, the dyes of this invention are desensitizing forconventional negative type photographic silver halide emulsions becausethey strongly desensitize such emulsions.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof, it willbe understood that variations and modifications can be elfected withinthe spirit and scope of the invention as described hereinabove, and asdefined in the appended claims.

We claim:

1. A composition of matter comprising an organic photoconductorspectrally sensitized with a cyanine dye comprising first and second 5-to 6-membered nitrogen containing heterocyclic nuclei joined together bya methine linkage selected from the group consisting of a dimethinelinkage and a trimethine linkage; the first of said nuclei beingselected from the group consisting of a pyrrolo [2,3-b]pyrazine nucleusand a pyrrolo[2,3-b1quinoxaline nucleus joined at the 3-carbon atomthereof to said linkage; and said second nucleus being selected from thegroup consisting of (a) a heterocyclic nitrogen containing nucleus ofthe type used in cyanine dyes when said linkage is a dimethine linkage;and, (b) when said linkage is a trimethine linkage, said second nucleusis selected from the group consisting of a 2-arylindole nucleus, apyrrolo [2,3-b1quinoxaline nucleus and a pyrrolo[2,3-b1pyrazine nucleus,each of said nuclei being joined at the 3-carbon atom thereof to saidtrimethine linkage, to complete said dye.

2. A composition as defined by claim 1 wherein said second nucleus ofsaid dye is an electron-accepting nucleus.

3. A composition as defined by claim 1 wherein said second nucleus ofsaid dye is selected from the group consisting of: a nitro substitutednucleus; an imidazo 1 4 [4,5-b1quinoxaline nucleus; a1,3,3-trialkyl-3H-pyrro1o [2,3-b1pyridine nucleus; and a 2-arylindolenucleus.

4. A composition as defined by claim 1 wherein said organicphotoconductor is selected from the group consisting of: a triarylamine;a 1,3,5--triphenyl-2-pyrazoline; a4,4'-bis(dialkylamino)-2,2'-dialkyltriarylamine; a 2,3,4,5-tetraarylpyrrole; and a 4,4'bis-dialkylaminobenzophenone.

5. A composition as defined by claim 1 which comprises from 1 to partsby weight of said photoconductor, said conductor being spectrallysensitized with from 0.1 to 10 parts by weight of said cyanine dye.

6. A composition of matter comprising an organic photoconductorspectrally sensitized with a cyanine dye wherein n represents a positiveinteger of from 1 to 2; L represents a methine linkage; R represents amember selected from the group consisting of an alkyl group, an alkenylgroup and an aryl group; R represents a member selected from the groupconsisting of an alkyl group and an aryl group; R and R each representsa member selected from the group consisting of a hydrogen atom, an alkylgroup, an aryl group, and together the nonmetallic atoms necessary tocomplete a pyrrolo[2,3-b] quinoxaline nucleus; R and R represent amember se lected from the group consisting of a hydrogen atom and anaryl group; R represents a member selected from the group consisting ofan alkyl group, an aryl group and a heterocyclic radical containing fromS to 6 atoms in the heterocyclic ring and having a hetero nitrogen,oxygen or sulfur atom; X represents an acid anion; D represents thenon-metallic atoms necessary to complete a nucleus selected from thegroup consisting of a 2- arylindole nucleus, a pyrrolo[2,3-b1pyrazinenucleus, and a pyrrolo[2,3-b]quinoxaline nucleus; and Z represents thenon-metallic atoms necessary to complete a nitrogen containingheterocyclic nucleus of the type used in cyanine dyes containing from 5to 6 atoms in the heterocyclic ring.

7. A composition as defined by claim 6 wherein said Z of said dyerepresents the non-metallic atoms necessary to complete anelectron-accepting nucleus.

8. A composition as defined by claim 6 wherein said Z of said dyerepresents the non-metallic atoms necessary to complete anelectron-accepting nucleus selected from the group consisting of anitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, anitrobenzoselenazole nucleus, a nitroindole nucleus, anirnidazo[4,5-b]nucleus, and a 1,3,3-trialkyl-3H-pyrrolo-[2,3-b]pyrridinenucleus.

9. A composition as defined by claim 6 wherein said R and R of said dyeeach represents a hydrogen atom.

10. A composition as defined by claim 6 wherein said R and R of said dyetaken together represent the nonmetallic atoms necessary to complete apyrrolo[2,3-b] quinoxaline nucleus.

15 11. A composition as defined by claim 6 wherein said organicphotoconductor has the following formula:

wherein each of D, E and G is an aryl group and J is selected from thegroup consisting of a hydrogen atom, an alkyl group and an aryl group,at least one of D. E and G containing an amino substituent selected fromthe group consisting of a secondary amino group and a tertiary aminogroup.

12. A composition as defined by claim .6 wherein said organicphotoconductor is selected from the group consisting of: triphenylamine;1,3,5-triphenyl-2-pyrazoline; 4,4 bis(diethylamino) 2,2dimethyltriphenylamine; 2,3,4,5 tetraphenylpyrrole; and, 4,4bis-diethylaminobenzophenone.

13. A composition as defined by claim 6 which comprises from 1 to 75parts by weight of said photoconductor, said photoconductor beingspectrally sensitized with from .01 to 10 parts by weight of saidcyanine dye.

14. A composition as defined by claim 13 wherein said organicphotoconductor and said dye are incorporated in an insulating binder.

15. A composition as defined by claim 13 wherein said organicphotoconductor and said dye are dispersed is from 25 to 99 parts byweight of a polyester of terephthalic acid and a glycol mixtureconsisting of a 9:1 weight ratio of 2,2'-bis [4-(2-hydroxyethoxy)phenyl]propane and ethylene glycol as insulating binder.

16. A composition of matter comprising from 1 to 75 parts by weight ofan organic photoconductor selected from the group consisting of:triphenylamine; 1,3,5-triphenyl 2 pyrazoline; 4,4 bis diethylamino 2,2-dimethyltriphenylmethane; 2,3,4,5 tetraphenylpyrrole; 4,4 bisdiethylaminobenzophenone; said organic photoconductor being spectrallysensitized with from .01 to 10 parts by weight of a dye selected fromthe group consisting of 1,3 diethyl 6 nitro 3 pyrrolo[2,3-b]quinoxalinothiacarbocyanine salt and 1,3 diallyl 1'- ethylimidazo[4,5-b1quinoxalino 3 pyrrolo[2,3-b] quinoxalinocarbocyanine salt.

17. A composition of matter as defined in claim 16 wherein said organicphotoconductor and said dye are dispersed in from 25 to 99 parts byweight of a polyester of terephthalic acid and a glycol mixtureconsisting of a 9:1 weight ratio of 2,2 bis [4-(2-hydroxyethoxy)phenyl]propane and ethylene glycol as insulating binder.

18. An electrophotographic element comprising a conductive supporthaving thereon a layer comprising an organic photoconductor in aninsulating binder, said organic photoconductor being spectrallysensitized with a cyanine dye selected from those comprising first andsecond 5- to 6-membered nitrogen containing heterocyclic nuclei joinedtogether by a methine linkage selected from the group consisting of adimethine linkage and a trimethine linkage; the first of said nuleibeing selected from the group consisting of a pyrrolo[2,3-b]-pyrazinenucleus and a pyrrolo[2,3-b]quinoxaline nucleus joined at the 3-carbonatom thereof to said linkage; and said second nucleus being selectedfrom the group consisting of (a) a heterocyclic nitrogen containingnucleus of the type used in cyanine dyes when said linkage is adimethine linkage; and (b) when said linkage is a trimethine linkage,said second nucleus is selected from the group consisting of a2-arylindole nucleus, a pyrrolo[2,3-b1quinoxaline nucleus and apyrrole[2,3-b]pyrazine nucleus, each of said nuclei being joined at the3-carbon atom thereof to said trimethine linkage, to complete said dye.

19. An electrophotographic element as defined in claim 18 wherein saidsecond nucleus of said dye is selected from the group consisting of: anitro substituted nucleus; an imidazo[4,5-b]quinoxa1ine nucleus; a1,3,3-

16 trialkyl-S'H-pyrrolo[2,3-b1pyridine nucleus; and, a 2-arylindolenucleus.

20. An electrophotographic element as defined in claim 18 wherein saidOrganic photoconductor is selected from the group consisting of: atriphenylamine; a 1,3,5-triaryl-2-pyrazoline; a4,4'-bis-(dialkylamino)-2,2'-dialkyltriarylamine; a2,3,4,5-tetraarylpyrrole; and a 4,4'-bisdialkylaminobenzophenone.

21. An electrophotographic element as defined in claim 18 wherein saidlayer comprises from 1 to parts by weight of said photoconductor, saidphotoconductor being spectrally sensitized with from .01 to 10 parts byweight of said cyanine dye.

22. An electrophotographic element comprising a con ductive supporthaving thereon a layer comprising an organic photoconductor spectrallysensitized with a dye selected from those represented by the followingformulas:

wherein n represents a positive integer of from 1 to 2; L represents amethine linkage; R represents a member selected from the groupconsisting of an alkyl group, an alkenyl group and an aryl group; -Rrepresents a member selected from the group consisting of an alkyl groupand an aryl group; R and R each represent a member selected from thegroup consisting of a hydrogen atom, an alkyl group, an aryl group, andtogether the nonmetallic atoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R and R represent a member se lected from the groupconsisting of a hydrogen atom and an aryl group; R represents a memberselected from the group consisting of an alkyl group, an aryl group anda heterocyclic radical containing from 5 to 6 atoms in the heterocyclicring and having a heteronitrogen, oxygen or sulfur atom; X represents anacid anion; D represents the non-metallic atoms necessary to complete anucleus selected from the group consisting of a 2-arylindole nucleus, apyrrolo[2,3-b]pyrazine nucleus and a pyrro1o[2,3-b]quinoxaline nucleus;and Z represents the non-metallic atoms necessary to complete a nitrogencontaining heterocyclic nucleus of the type used in cyanine dyescontaining from 5 to 6 atoms in the heterocyclic ring.

23. An electrophotographic element as defined in claim 22 wherein said Zof said dye represents the non-metallic atoms required to complete anelectron-accepting nucleus.

24. An electrophotographic element as defined in claim 22 wherein said Zrepresents the non-metallic atoms required to complete anelectron-accepting nucleus selected from the group consisting of anitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, anitrobenzoselenazole nucleus, a nitroindole nucleus, animidaz0[4,5-b]quinox aline nucleus, and a1,3,3-trialkyl-3H-pyrrolo[2,3-b] pyridine nucleus.

25. An electrophotographic element as defined in claim 22 wherein said Rand R of said dye each represents a hydrogen atom.

26. An electrophotographic element as defined in claim 22 wherein said Rand R of said dye taken together represent the non-metallic atomsnecessary to complete a pyrrolo[2,3-b]quinoxaline nucleus.

27. An electrophotographic element as defined in claim 22 wherein saidorganic photoconductor has the following formula:

wherein each of D, E and G is an aryl group and J is selected from thegroup consisting of a hydrogen atom, an alkyl group and an aryl group,at least one of D, E and G containing an amino substituent selected fromthe group consisting of a secondary amino group and a tertiary aminogroup.

28. An electrophotographic element as defined in claim 22 wherein saidorganic photoconductor is selected from the group consisting of:triphenylamine; 1,3,5-triphenyl- 2 pyrazoline;4,4'-bis-(diethylamino)-2,2-dimethyltriphenylarnine;2,3,4-5-tetraphenylpyrrole; and 4,4'-bis-diethylaminobenzophenone.

29. An electrophotographie element as defined in claim 22 wherein saidlayer comprises from 1 to 75 parts by weight of said photoconductor,said photoconductor being spectrally sensitized with from .01 to partsby weight of said cyanine dye.

30. An electrophotographic element as defined in claim 29 wherein saidorganic photoconductor and said dye are incorporated in an insulatingbinder.

31. An electrophotographic element as defined in claim 30 wherein saidorganic photoconductor and said dye are dispersed in from 25 to 99 partsby weight of a polyester of terephthalic acid and a glycol mixtureconsisting of 9:1 weight ratio of 2,2-bis-[4-(2-hydroxyethoxy)-phenyl]-propane and ethylene glycol as insulating binder.

32. An electrophotographic element comprising a conductive supporthaving thereon a. layer comprising from 1 to parts by weight of anorganic photoconductor selected from the group consisting of:triphenylamine; 1,3,5-triphenyl-2-pyrazoline;4,4-FDis-diethylamino-2,2'-dimethyltriphenylmethane;2,3,4,5-tetraphenylpyrrole; 4,4- bis-diethylaminobenzophenone; saidorganic photoconductor being spectrally sensitized with from .01 to 10parts by weight of a dye selected from the group consisting of 1,3diethyl-6'-nitro3-pyrrolo[2,3-b]quinoxalinothiacarbocyanine salt and1,3-diallyl-1-ethylimidazo- [3,4-b]quinoxalino 3 pyrrolo[2,3-b]quinoxalinocarbocyanine salt.

33. An electrophotographic element as defined in claim 32 wherein saidorganic photoconductor and said dye are dispersed in from 25 to 99 partsby Weight of a polyester of terephthalic acid and a glycol mixtureconsisting of a 9:1 weight ratio of2,2-bis-[4-(2-hydroxyethoxy)-phenyl]-propane and ethylene glycol asinsulating binder.

References Cited UNITED STATES PATENTS 2,927,026 3/ 1960 Heseltine etal. 96105 3,132,942 5/1964 Stewart 961 3,143,544 8/1964 Van Dormael260-240 3,314,796 4/1967 Gotze et al. 96101 3,326,688 6/1967 Jenkins etal. 96102 3,455,684 7/1969 Depoorter et al. 961.7 3,468,661 9/ 1969Libeer et al. 96-1.7

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant ExaminerUS. Cl. X.R.

